Resonators have been widely used in microwave and millimeter wave circuits such as filters, oscillators and antennas, for example. These components comprise important parts of many wireless systems and devices, although their uses are not confined to wireless applications.
It is also known that a dielectric resonator (DR) can be used as a circuit element in oscillator and filter circuits, or as an effective radiator that is now commonly known as a DR antenna (DRA). In the past two decades, the DRA has been studied extensively due to a number of advantages it provides such as its small size, low loss, low cost, light weight, and ease of excitation. DRAs are miniaturized antennas of ceramics or other dielectric media for microwave frequencies. DRAs are fabricated entirely from low loss dielectric materials and are typically mounted on ground planes. Their radiation characteristics are a function of the mode of operation excited in the DRA. The mode is generally chosen based upon operational requirements. DRAs offer several advantages over other antennas, such as small size, high radiation efficiency, and simplified coupling schemes for various transmission lines. The bandwidth can be controlled over a wide range by the choice of dielectric constant, and the geometric parameters of the resonator.
By using a dielectric resonator (DR), a size of an antenna can be scaled down by roughly a factor of 1/√{square root over (∈r)}, where ∈r is the dielectric constant of the DR element material. This can be very useful in reducing the antenna size, particularly in wireless communication applications. Today, compactness has become one of the topmost priorities in developing wireless communication devices and systems, supporting the development of multifunction components to miniaturize the devices and systems. As a result, there has been a trend to bundle several microwave functions into a single module, e.g. to combine several microwave resonators to provide multiple functions. It has also been shown to design a microstrip single-resonator balun-filter. Furthermore, it has recently been shown to design an antenna and filter using a single DR. Also, it has been demonstrated that the DRA can be integrated with an oscillator circuit.
With the advent of the ultrawide-band and millimeter-wave era, it has become increasingly normal to combine microwave and optical circuits in modern communication systems. The transparent microstrip antenna has been studied for optical applications, but having a highly conducting transparent film is still a challenging problem. As the conductivity of the conductive transparent film (˜5×105 S/m) is relatively low as compared with that of metals, most of the transparent planar antennas reported thus far have an antenna gain of lesser than 0 dBi. It has been proposed to apply conductive paste to the slot edge of the transparent microstrip antenna for improving the radiation efficiency. Using this technique, the antenna gain has been increased from about −5 dBi to ˜0 dBi, but at the cost of reducing the transparency of the antenna.
Several studies on the integration of planar antennas and solar cell panels have also previously been reported. The integration of a microstrip antenna and a solar cell panel usually causes the antenna gain to degrade significantly, although recent efforts have advanced the technology to increase the antenna gain of the solar-cell-integrated (metallic) microstrip antenna to ˜1.05 dBi. However, this is still ˜6 dB lower than that of metallic microstrip antennas. Moreover, the effective illumination area of the solar cell panel is somewhat reduced because of introducing the non-transparent microstrip antenna. In order to solve this problem, it has been proposed to use a slot antenna, but this requires a removal of part of the solar cell panel which is undesirable.